Driven accessories in a vehicle may include, for example, an air conditioning compressor, a power steering pump, and an alternator. These accessories are generally powered by output from the engine. Conventional automotive accessory drive systems include a drive pulley connected to an engine output shaft. A flexible chain or belt couples the drive pulley with a plurality of driven pulleys that are each operatively connected to an accessory. The operating speeds of the accessories in such a conventional drive system are directly proportional to the speed of the engine. Since the engine operates over a wide speed range (i.e., for example, between 500 rpm and 7,000 rpm), the accessories are typically designed to provide full capacity at the low end of the engine speed range in order to ensure that they remain operational. Therefore, at higher engine speeds, excess energy transferred to the accessories may be lost.